Electric lamps and method of detecting leaks in such lamps



Oct. 22, 1968 c. L. PETERSON 3,407,123

ELECTRIC LAMPS AND METHOD OF DETECTING LEAKS IN SUCH LAMPS Filed May 29, 1964 CARL L. PETERSON INyENTOR. Q

AT RNEY ABSTRACT OF THE DISCLOSURE A method and apparatus for testing oxygen leak in electric lamps, wherein a silver coating is placed inside the lamp at a location viewable from the exterior of said lamp. An electric discharge is applied to the lamp from the outside, whereby any oxygen leaking into the lamp will cause the silver coating to turn brownish-black.

This invention relates to electric lamps and particularly to the use of an indicator in such lamps to determine the presence of leaks in the envelope. Furthermore, this invention relates to the testing of such lamps to determine if the envelope has leaked.

This invention has particular applicability to high pressure electric discharge devices, commonly called mercury lamps. Such lamps generally include a quartz arc tube supported upon -a metal harness and enclosed within an outer bulbous envelope. Usually, the outer envelope is filled with about /2 atmosphere of an inert gas such as nitrogen. Oxygen is excluded. If the envelope has or subsequently develops a leak, atmospheric oxygen will enter and destroy the arc tube rather quickly. The oxygen reacts with the metal parts in the press seals in the ends of the arc tube to oxidize them and cause the quartz to crack. Heretofore, it was ditiicult, if not impossible, to detect the presence of such leaks immediately after manufacture. Frequently the leaky lamps would fail within one or two hundred hours of operation in the field since it took this time for the reaction between the metal and the oxygen to reach serious proportions.

According to my invention I have discovered a means for detecting such leaks in a very reliable manner. This means is a coating of silver disposed within the envelope and visible to the outside with a gas space between the viewable surface and the envelope. Preferably the silver is applied as a metal coat or a dab of silver paste upon the metal frame which holds the arc tube. I have discovered that when the silver is exposed to a high frequency, high voltage electric discharge applied from the outside of the envelope, it turns brownish-black if oxygen has leaked in. If oxygen has not entered, the coating is unaffected.

Accordingly, the primary object of my invention is to test for the presence of oxygen within electrical lamps.

A further object of my invention is to detect oxygen within the outer jackets of high pressure electric discharge devices.

A feature of my invention is placing a coating of silver within the envelope and exposing such silver to a high frequency, high voltage electric discharge to detect if oxygen has entered.

An advantage of my invention is that leaky lamps can be discovered in the factory before they are sold.

Many other objects, features and advantages of the present invention will become manifest to those conversant with the art upon making reference to the detailed description which follows and the accompanying sheet of drawing in which preferred embodiments of an electric discharge device having an indicating means are shown United States Patent and described and wherein the principles of the present 3,407,123 Patented Oct. 22, 1968 ice The figure is an elevational view of a high pressure electric discharge device illustrating the positioning of an electric discharge are tube disposed within an outer bulbous envelope and the indicator.

Referring to the figure, an elevational view of a high pressure electric discharge device is shown. The device comprises an outer vitreous envelope 2 of generally tubular form having a central bulbous portion 3. The envelope 2 is provided at its ends with a re-entrant stem having a press through which extend relatively stiff lead-in wires 6 and 7 connected at their outer ends to the electrical contacts of the usual screw type base 8 and at their inner ends to the arc tube and the harness.

The are tube is generally made of quartz although other types of glass such as alumina or Vycor can be used, the latter being a glass of substantially pure silica. Sealed in the arc tube 12 at the opposite ends thereof are main discharge electrodes 13 and 14 which are supported on lead-in wires 4 and 5 respectively. Each main electrode comprises a core portion which may be a prolongation of the lead-in wires 4 and 5 and may be prepared of suitable metal such as for example, molybdenum or tungsten. The prolongations of these lead-in wires 4 and 5 can be surrounded by molybdenum or tungsten wire helixes.

An auxiliary starting probe or electrode 18, generally prepared of tantalum or tungsten is provided at the base end of the arc tube 12 adjacent the main electrode 14 and comprises an inwardly projecting end of another lead-in wire.

Each of the current lead-in wires described have their ends welded to intermediate foil sections of molybdenum which are hermetically sealed within the pinched sealed portions of the arc tube. The foil sections are very thin, for example approximately 0.0008 inch thick and go into tension without rupturing or scaling off when the heated arc tube cools. Relatively short molybdenum wires 24, 23 and 35 are welded to the outer ends of the foil and serve to convey current to the various electrodes inside the arc tube 12. If oxygen has leaked into the jacket these metal parts will oxidize, the reaction rate being raised substantially by the heat of the arc tube during operation.

Metal strips 45 and 46 are welded onto the lead-in wires 23 and 24 respectively. A resistor 26 is welded to foil strip 45 which in turn is welded to the arc tube harness. The resistor may have a value of for example 40,000 ohms and serves to limit current to auxiliary electrode 18 during normal operation of the lamps. Metal foil strip 46 is welded directly to stiff lead-in wire 7. Lead-in wire 35 is welded at one end to a piece of molybdenum foil sealed in the arc tube 12 which in turn is welded to main electrodes 13 and 14. Metal foil strip 47 is welded to one end of lead-in 35 and at the other end to the harness. The pinched or flattened end portions of the arc tube 12 form a seal which can be of any desired width and can be made by flattening or compressing the ends of the arc tube 12 while they are heated. The are tube 12 is provided with a filling of mercury in a quantity sufficent to be vaporized completely when a pressure in the order of one half to several atmospheres is reached during normal lamp operation at temperatures of 450 to 700 C.

The U-shaped internal wire supporting assembly or arc tube harness serves to maintain the position of the arc tube 12 substantially coaxially within the envelope 2. To support the arc tube 12 within the envelope, stiff leadin wire 6 is welded to the base 53 of the harness. Because stiff lead-in wires 6 and 7 are connected to opposite sides of a power line, they must be insulated from each other together with all members associated with each of them. Clamps 56 and 57 hold the arc tube 12 at the end por- 3 tions and are fixedly attached to legs 54 of theharness. A rod 59 bridges the free ends of the U-shaped support wire 54 and is fixedly attached thereto for imparting stability to the structure. The free ends of the U-shaped wire 54 are also provided with a pair of metal leaf springs 60, frictionally engaging the upper tubular portion of the lamp envelope 2. A heat shield 61 is disposed beneath the arc tube 12 and above the resistor 26 to protect it from excessive heat generated during lamp operation. 7

The silver coating of my invention can be applied anywhere within the envelope so long as there can be a gas (including the oxygen if the lamp leaks) betweenthe outside of the lamp and the surface to be tested. Preferably, for example, the silver is disposed upon the springs 60 as a coating 62 while, of course, it could be placed upon the heat shield 61 or elsewhere. The size of the testing surface is not critical so long as it is large enough to be seen.

When testing the lamp for the presence of oxygen, the coating is exposed through the envelope glass to a high voltage, high frequency electric discharge. The discharge can be produced, for example, by a spark or Tesla coil such as the unit sold by the Ecco High Frequency Corp., Model 6-4. The current is in the order of microamperes and the frequency in the order of one megacycle, thus minimizing any danger to the operator. A high leakage transformer also, can be used to generate the spark discharge. Such devices operate at about 60 cycles per second and the current is quite small, generally about milliamperes.

If oxygen from the atmosphere has leaked into the outer envelope, the silver will turn brownish-black when the outside of the envelope is exposed to the spark discharge which arcs through to the glass and onto a metal surface and particularly to the silver when the arc is directed that way. Lamps havin silver which turns brownish-black can be rejected. The are discharge within leaky envelopes form ozone which immediately reacts with the silver to form the brownish-black oxide.

It is apparent that modifications and changes may be made within the scope of the instant invention. It is my intention however to be limited only by the scope of the appended claims.

As my invention I claim:

1. A method of testing electric lamps having a transparent envelope to determine the presence of leaks the steps which comprise: applyinga coating of silver within said envelope, the surface of said silver being viewable from the exterior of said lamp and being disposed so that a gas space is present between the viewable surface and the interiorwall of said envelope; producing an arc discharge from without said envelope and adjacent said silver to thereby darken said silver coating when oxygen is present in said lamp.

2. A method of testing electric lamps having a transparent envelope to detect the presence of leaks, the steps which comprise: applying a coating of silver within said envelope, the surface of said silver being viewable from the exteriorof said lamp and bein disposed so that a gas space is present between the viewable surface and the interior wall of said envelope; generating ozone when oxygen is present in said envelope, said generation being from external arc and adjacent said silver coating to thereby darken the silverto indicate the presence of oxygen.

3. A method of testing high'pressure electric discharge devices contain an arc tube with electrodes disposedat either end thereof, said are tube being supported upon a metal harness, said are tube andharness being enclosed withiii an outer bulbous transparentenvelope, the steps which comprise: applying a coating of externally visible silver to said metal harness; producing an externally initiated arc discharge within said envelope adjacent said silver to thereby darken said silver coating when oxygen is present in said lamp.

4. An electric lamp comprising: a glass envelope; means to generate light within said envelopeya silver coating disposed within said envelope, the surface of said silver coating being viewable from the exterior of s'aid lamp and said coating being disposed so that a gas space is present between the viewable surface and the interior wall of said envelope; said-silver coating being an oxygen detecting means and being spaced apart from the walls of said envelope.

5. A high pressure electric, discharge device comprising: an arc tube having electrodes disposed at either end thereof; a metal harness for holding said are tube;means to convey electricity to said electrode in said are tube and an outer bulbous envelope disposed about said harness and are tube; a silver coating upon said metalharness, said silver coating being an oxygen detecting means. I 6. In a method of testing electric lamps, having a transparent envelope, to detect the presenceof leaks, the steps which comprise: applying an externally visible coating of silver within said envelope; producing an are ,discharge from without saidenvelope adjacent said silver to thereby darken said silver coating when oxygen is present in said lamps.

7. A method of testing high pressure electric discharge devices containing an arc tube with electrodes disposed at either end thereof, said are tube being supported upon a metal harness, said are tube and harness being enclosed within an outer bulbous transparent envelope, the steps which comprise: applying a coating of externally visible silver to said metal harness; generating ozone when oxygen is present in said envelope, said generation-originating from without said envelope and extending adjacent said silver coating to thereby darken the silver to indicate the presence of oxygen.

References Cited UNITED STATES PATENTS 533,502 2/1895 Smith et a1. 73 40 1,014,287 1/1912 Erskine 73 40 2,251,992 8/1941 Flory et a1. 204 1s1 2,507,321 5/1950 Sherwood. 3,237,284 3/1966 Bird '-313 315 3,262,756 7/1966 Keilholtz et al. 23-232 HOWARD S. WILLIAMS, Primary Examiner. T. TUNG, Assistant Examiner. 

